Question

Write the formula for each of the following compounds: (a) Diamminesilver(I) nitrate (b) Potassium diaquadioxalatocobaltate(III) (c) Hexacarbonylmolybdenum(0) (d) Diamminebis(ethylenediamine) chromium(III) chloride

Short answer

(a) [Ag(NH₃)₂]NO₃ (b) K[Co(H₂O)₂(C₂O₄)₂] (c) [Mo(CO)₆] (d) [Cr(NH₃)₂(en)₂]Cl₃

Step-by-step solution

Identify each component of the compound

Break down the names of each compound to identify the metal, ligands, charge or oxidation state, and other components that will form the formula.

Write the chemical formula for Diamminesilver(I) nitrate

For Diamminesilver(I) nitrate, the ligand is ammonia (NH₃), silver is Ag with a 1+ charge, and nitrate is NO₃⁻. The complex can be written as [Ag(NH₃)₂]NO₃.

Write the chemical formula for Potassium diaquadioxalatocobaltate(III)

For Potassium diaquadioxalatocobaltate(III), the oxidation state of cobalt is +3, it is coordinated to two water (H₂O) and two oxalate (C₂O₄²⁻) ligands. The complex becomes K[Co(H₂O)₂(C₂O₄)₂].

Write the chemical formula for Hexacarbonylmolybdenum(0)

For Hexacarbonylmolybdenum(0), Molybdenum (Mo) is coordinated to six carbonyl (CO) ligands with an oxidation state of 0. Therefore, the formula is [Mo(CO)₆].

Write the chemical formula for Diamminebis(ethylenediamine) chromium(III) chloride

For Diamminebis(ethylenediamine) chromium(III) chloride, chromium is coordinated to two ammonia (NH₃) and two ethylenediamine (en) ligands in the +3 oxidation state. The resulting formula is [Cr(NH₃)₂(en)₂]Cl₃.

Key concepts

Chemical Formulas

When creating chemical formulas for coordination compounds, it is essential to decode the chemical names given. You should identify the central metal atom or ion, the oxidation state, and the attached ligands. For example, in Diamminesilver(I) nitrate, 'Diammine' means two ammonia (NH₃) ligands are attached to a silver ion. The oxidation state of silver here is +1, indicated by the Roman numeral I in parentheses. Consequently, the formula is written with the complex ion in square brackets:

• [Ag(NH₃)₂]
• NO₃ outside the brackets represents the nitrate part of the compound.

Order and brackets play crucial roles in expressing these relationships correctly.

Nomenclature

Understanding nomenclature is key for writing formulas for coordination compounds. Each part of a compound's name provides specific details:

• The prefix indicates the number of each type of ligand (e.g., 'di-' for two).
• The name of the ligands comes before the metal's name.
• Oxidation states are expressed in Roman numerals in parentheses after the metal's name.

Hence in Potassium diaquadioxalatocobaltate(III), 'potassium' refers to the counter ion. 'Diaqua' means two water molecules act as ligands, 'dioxalato' means two oxalate ions, and the number in parentheses signifies cobalt's oxidation state.

Ligands

Ligands are ions or molecules that donate an electron pair to the central metal atom or ion in coordination compounds. They are crucial in defining the structure and properties of the compound. For example, in Hexacarbonylmolybdenum(0), 'hexacarbonyl' indicates six carbon monoxide (CO) ligands.

• Neutral ligands like H₂O and NH₃ do not affect the net charge of the complex.
• Charged ligands such as C₂O₄²⁻ (oxalate) do affect charge balance.

In coordination chemistry, ligands can be monodentate (attaching at one site) like CO, or polydentate (attaching at multiple sites), such as ethylenediamine.

Oxidation States

Oxidation states in coordination compounds denote the charge of the central metal ion after electrons have been donated by the ligands. It's depicted in Roman numerals. For example, in Diamminebis(ethylenediamine) chromium(III) chloride, chromium is in a +3 state.

• This guides the formula as it determines the number and type of ligands needed for charge balance.
• The counter ions outside the complex, like Cl⁻ in this case, adjust to neutralize the overall charge of the compound.

Identifying the oxidation state helps in accurately writing and balancing chemical formulas.